The present invention relates to apparatus for making perforations in web- or sheet-like materials, and more particularly to improvements in apparatus for making perforations in wrapping materials for rod-shaped articles of the tobacco processing industry. Still more particularly, the invention relates to improvements in apparatus for making perforations in wrapping materials for tobacco and/or filter material by means of one or more beams of coherent radiation. The wrapping material which is to be perforated in the apparatus of the present invention can be used to confine natural, substitute or reconstituted tobacco, filter material and/or tobacco as well as filter material.
The making of air-permeable ventilation zones in the wrappers of filter cigarettes and other types of rod-shaped smokers' products is known for many years. For example, commonly owned U.S. Pat. No. 4,090,826 to Hinzmann discloses an apparatus which utilizes pointed tools serving to pierce the wrappers of filter plugs of filter cigarettes so as to form therein ventilation zones which permit atmospheric air to penetrate into the column of tobacco smoke and to thus exert a beneficial influence upon the percentage of nicotine and condensate in the smoke which reaches the smoker's mouth. The perforations in a filter cigarette are or can be made in the wrapper of the filter mouthpiece close to the locus of attachment of the mouthpiece to the tobacco-containing portion of the article. It is desirable to ensure that the permeability of the ventilating zone match or very closely approximate a preselected value and that the selected permeability remain constant for any desired periods of time. In other words, the ratio of fresh air to other constituents of the column of tobacco smoke flowing toward the mouth of the smoker should remain unchanged from article to article in spite of the extremely high speed at which such articles are being turned out by a modern filter rod making machine, cigarette maker or filter tipping machine.
The apparatus which is disclosed in the aforementioned patent to Hinzmann exhibits the drawback that the mechanical piercing tools are subject to extensive wear so that their positions relative to the advancing wrapping material must be changed at rather frequent intervals. Furthermore, it is necessary to replace a set of piercing tools with a set of fresh tools as soon as mere adjustment of the positions of partially spent or dulled piercing tools does not sufficient to ensure the making of holes having a predetermined diameter. This entails relatively long interruptions of production which, in turn, results in substantial losses in output since a modern filter tipping machine, cigarette maker or filter rod making machine can turn out many thousands of articles per minute. Moreover, the means for adjusting the positions of piercing tools relative to the path of movement of wrapping material and for causing penetration of such tools into the wrapping material whenever the tools are to form a ventilation zone is rather complex, bulky and expensive.
It is also known to utilize sets of electrodes which cause partial combustion of wrapping material to thus generate holes of desired size and/or shape. Still further, it is already known to employ perforating apparatus which comprise one or more sources of coherent radiation. One or more beams of such radiation are directed against the wrapping material so that the beam or beams combust the material and make holes which allow fresh air to penetrate into the column of tobacco smoke. Reference may be had to U.S. Pat. No. 4,240,448 to Heitmann; to U.S.Pat. No. 4,121,595 to Heitmann; to U.S. Pat. No. 4,193,409 to Wahle et al.; to U.S. Pat. No. 4,281,670 to Heitmann et al.; and to U.S. Pat. No. 4,249,545 to Gretz et al. The just enumerated patents disclose lasers which are energized at intervals so as to ensure that the beams of coherent radiation will make discrete hole instead of burning away entire strips of wrapping material.